1. Field of the Invention
The present invention relates to a transmission and a motor or non-motor type transport device including a cross-coupling power train using the transmission, such as chainless bicycle or wagon with two or four wheels.
2. Background of the Related Art
A transport device such as bicycle or wagon is self-propelled, and is classified into a non-motor type which transmits a pedal force to a rear wheel(s) via a pedal, a crank arm and a chain, and a motor type which transmits a driving force from an engine to a rear wheel(s) via a chain.
Such a transport device is necessarily provided with a power train for transmitting a pedal force or a driving force of an engine to a rear wheel(s) in order for its operation.
The power train of the transport device includes a transmission for increasing the pedal force or the driving force of the engine and increasing or reducing speed to change a gear ratio in accordance with road conditions or operation. The transmission employs sprockets of various sizes which are arranged in order, and chains for connecting the sprockets.
The construction of the transmission employing the sprockets and the chains is complicated and is limited to a shift range. Also, since the driving force is not smoothly transmitted by the chains connecting the sprockets which are arranged in order, the shift change is not smoothly and quickly performed.
More specifically, in case where the shift is performed from a high stage to a low stage or vice versa while skipping over an adjacent stage, the shift operation should pass through sprockets arranged between both gearshifts, as described above. Also, since a traveling distance should be required for the sequential shift process, it is not easy to instantaneously change the gearshift at low or high speed, for example, on a sloping road.
Although the traveling to operate the transmission using the multi-stage sprocket and chain is not out of the question on a flat road, the shift is not smoothly performed on an uphill road or downhill road, thereby inefficiently transmitting the driving power and thus causing unnecessary energy loss. Also, the transport device cannot travel on a steep or irregular slope, which deteriorates the performance of the transport device.
In order to improve the construction of a power transmission system and reducing the power loss, power trains for a chainless transport device have been developed. One example of the power trains is a bicycle using a cross-coupling power train.
More specifically, a cross-coupling power train including a bevel gear or a crown type gear and a roller type gear is installed between a main shaft of a crank arm and a rear wheel to transmit the driving force from the crank arm to the rear wheel.
Also, the cross-coupling power train includes a transmission operated by the shift lever which is provided on a handle bar, so as to drive the bicycle by properly shifting the transmission in accordance with conditions of travel roads, such as a flat road or slope road. In this instance, the transmission of the power train includes a cross-coupling power transmitting system, planetary or sun gears, or large and small spur gears which are arranged in a multi-stage and are sequentially connected to each other to change the speed.
However, the transmission has a narrow shift range, in which a shift stage is gradually moved at a constant ratio within a certain shift width. Also, under the specific traveling conditions requiring for spontaneous low-speed shift on a slope road, the shift operation of the transmission is not easily performed due to the required traveling distance or strong load.
Also, the power transmission is not effectively performed since the proper shift is not carried out on the slope road, so that the bicycle does not properly travel. In case of a mountain area having an irregular steep slope which requires a large shift ratio, a driver stops off the bicycle since the speed does not changed by strong torque and low rotation at a low-speed stage.
In the transmission applied to the power train for transport devices such as bicycle or wagon, the torque is maximized at a constant speed, while strong torque and low rotation are required at initial drive or on a slope road. As the speed is increased, the transmission increases the rotation rather than the torque. The low- or high-speed shift operation should be quickly carried out in accordance with the traveling conditions, in particular, on an uphill or downhill road.
In case of mountain bikes, the low-speed shift of low rotation and strong torque is required on a mountain area including irregular and steep slopes, but the shift is not properly performed to make the continuous travel impossible.